In operation, both two and four-stroke cycle diesel engines generate what is known in the art as "blow-by gases", or combustion gases which during the compression and firing strokes of a piston blow past compression ring seals surrounding the piston, and subsequently down between a cylinder wall and the piston sidewall. The volume of this blow-by gas is generally less than 2% of the cylinder displacement.
In diesel engines powered by fuels containing abrasive particles, for example a coal-water slurry fuel, these blow-by gases contain abrasive particulate matter (for example, ashes). When this abrasive particulate matter blows past the compression ring seals, it subsequently causes excessive wear of the piston wall, cylinder sidewall (or liner) and compression ring seals, and eventually premature failure of the diesel engine. Accordingly, it would be desirable to provide a diesel engine wherein dirty combustion gases are prevented from blowing by the compression ring seals. Such an engine would be subject to substantially less wear due to the abrasion described above, and would exhibit better reliability over an increased lifespan.